Atherosclerosis and heart disease remain a leading cause of death in the United States. Early events in formation of atherosclerotic plaques in the vessel wall include oxidation of lipid, activation of endothelial cells in microenvironments of the vessel, and recruitment and adhesion of monocytes to the vessel wall. Recent studies using mouse models of atherosclerosis have identified the 12/15 lipoxygenase enzyme (12/15 LO) as having a major role in atherosclerosis development. This application explores the mechanisms by which 12/15 LO regulates monocyte:endothelial interactions and contributes to atherosclerosis. Both in vitro and in vivo approaches will be utilized. We have recently generated 12/15LO transgenic mice on a C57BL/6J background that have a 2-fold increase in 12/15LO activity. The 12/15LO transgenic mice show changes in expression of specific endothelial selectins, adhesion molecules and chemokines that regulate monocyte adhesion. We will use these 12/15 LO transgenic mice as well as 12/15 LO knockout mice to address the specific aims of the proposal. Aim 1 will identify key chemokines, integrins, and adhesion molecules that are regulated by 12/15 LO activity in primary monocytes and endothelial cells isolated from 12/15LO transgenic and 12/15LO knockout mice. Aim 2 will test whether 12/15 LO activity in the monocyte or the endothelial cell regulates monocyte:endothelial interactions. Aim 2 will also measure the contribution of 12/15 LO activity on functional parameters of monocyte rolling, arrest, and adhesion. Aim 3 will identify the cellular sources of the factors important for atherogenesis in vivo in mice that vary in their 12/15LO activity. Aim 3 will utilize novel approaches to monitor monocyte trafficking using both fluorescent and gamma camera imaging of labeled monocytes in vivo. We will also use bone marrow transplantation to identify whether 12/15 LO activity in monocyte or endothelial cell contributes to atherosclerosis in vivo. These studies should greatly enhance our understanding of the mechanisms by which 12/15 LO modulates atherosclerosis development in vivo. The therapeutic significance of these studies lies in the fact that 12/15LO activity is elevated in diabetic animals. Also, the identification of factors that regulate monocyte adhesion to atherosclerotic plaques could provide a rationale for developing new therapies to inhibit this disease.